Electrical instrument.



H. A. EWEN.

ELECTRICAL INSTRUMENT.

APPLICATION FILED MAY 1s. 1911.

lutentd Feb. 11, 1919.

UNITED STATES PATENT OFFICE.

HARRY ALEXANDER EWEN, OF LONDON. ENGLAND, ASSIGNOR TO MARCONI'WIRELESS TELEGRAPH COMPANY 0F AMERICA, OF NEW YORK., N. Y., A CORPORATION 0F NEW JERSEY.

Application led May 16, 1917.

1' 'o all lf/1.0m t may concern.'

lle it known that I, Hanni' ALEXANDER Ewan, a subject of. the King of Great Britain, residing at Marconi House, Strand, London, England. have invented a new and useful Improvementjn Electrical Instruments. of which thc following is a specification. a.

This invention relates to electrical instruments which depend for their action upon the expansion of one or more filaments due to the heating effect of electrical currents. Such instruments may be used to measure the strength or the voltage of the current, or as relays.

The invention is illustrated by the accompallying drawing. which shows a current meter constructed somewhat in the form of an electric light bulb.

A is a glass bulb provided with a socket B; in this socket is mounted a frame C formed of glass and supporting,r a bracket D in which is mounted an arbor E connected to one end of a spiral spring F, the other end of which is connected to the bracket. Fast on the arbor is an arm G the ends of which move Within scales H upon the exterior of the bulb A. Through holes in the arm is threaded a conducting filament I the ends of which are secured to leads J which pass through the base of the frame C and are connected to terminals K.

When the terminals are connected to an electric circuit. a current passes through the filament and heats it, and the filament thereby expands and allows the spring to rotate the arbor so thatl the ends of the arm G move around the scales.

' I have found that the sensitiveness of the instrument and the amount of current it will register are greatly affected by the density and the nature of the gas contained in the' bulb. I therefore evacuate the bulb so Specification of Letters Patent.

Patented Feb. 11, 1919.

Serial No. 168,998.

that the air contained therein is extremely rarefied. 4By this means I greatly increase the sensit-iveness of the instrument.

In some cases also, after exhausting the air. I pass into the bulb a small quantity of hydrogen or other heat conducting gas. and I find that when this has been done I obtain two important results as compared with the case of where the bulb is filled with air or Where it is totally exhausted: one is that the angle through which the arm is turned on the passage of a current of a definite strength. is considerably diminished so that the instrument is `capable of measuring a larger current. While the other is that the rate of Working of the instrument is enhanced, that is to say, the arm G attains its position of rest much more quickly after the application of the current.

It will be noted that the arbor E is mounted against longitudinal movement, and that the arm G is symmetrical With respect to said arbor. As a result. it is apparent that this instrument will operate equally Well and with equal accuracy irrespective of the position or plane in which it is placed.

What I claim is Thecornbination of a vessel from which the air has been exhausted and which contains hydrogen under reduced pressure, a scale, an arbor rotatably mounted in the vessel, an arm fast upon the arbor and adapted to move over' the scale, a filament stretched between the arm and a fixed point Within the vessel.y means for controlling the movement of the arbor and connection whereby an electric current may be passed through said filament to heat the same.

In testimony that I claim the foregoing as my invention. I have signed my name this third day of A ril` 1917.

HARRY A EXANDER EWEN. 

